While Liam Neeson's Qui-Gon Jinn might have been murdered by Darth Maul in The Phantom Menace, the Jedi Master was still a crucial part of Star Wars even after his death. Being one of the few Jedi to retain his individual consciousness within the Cosmic Force, Qui-Gon was made himself known and influenced the course of the Skywalker saga a handful of times from beyond the grave. Not only did he guide Yoda and his former Padawan Obi-Wan Kenobi into new their new roles during the original trilogy of films and beyond, but he also served as a key motivator in the final film of the Skywalker saga as well.
Because of Qui-Gon Jinn and his unique awareness of the Force beyond other members of the Jedi Order, it makes sense that fate would lead him to the discovery of Star Wars' prophesized Chosen One, Anakin Skywalker, the one who would bring balance to the Force. His role in shaping the course of the galaxy didn't end after his death. If anything, Qui-Gon was able to do more in death than he achieved in life, helping his fellow Jedi as they prepared for the new hope that would come to the galaxy after the Republic's fall.
While Qui-Gon has had a handful of canonical appearances on-screen after his death, there have also been novels (such as A Certain Point of View) that have confirmed his presence in Star Wars on both Dagobah and Tatooine where Yoda and Obi-Wan were respectively in exile during the Empire's rule. While this does create an opportunity for Liam Neeson to reprise his role once more in the upcoming Obi-Wan Kenobi series, that's yet to be confirmed. In any case, here's every appearance of Jedi Master Qui-Gon Jinn after his death (thus far).
Attack of the Clones: Qui-Gon Jinn's Voice During Anakin's Tusken Raider Massacre
Following Qui-Gon's defeat in Star Wars: The Phantom Menace, Obi-Wan Kenobi promised his master that he would train Anakin Skywalker. In Attack of the Clones, ten years have passed and Anakin has become a powerful Jedi as Obi-Wan's apprentice, protecting Senator Padmé Amidala while his master tracks down her attempted assassin prior to the start of The Clone Wars. However, Padmé agrees to go with Anakin back to his homeworld of Tatooine after he starts having visions of his mother suffering and in pain.
Upon their arrival to the desert world, Anakin learns that his mother was abducted by Tusken Raiders. Finding her just before her death, Anakin's grief turns to rage and he slaughters the entire tribe, his massacre serving as his first major step towards the dark side of the Force. During his killing, Qui-Gon's voice can be heard yelling out Anakin's name: "Anakin, Anakin, no!" This would also be the first confirmation that Qui-Gon had retained his consciousness after death.
Clone Wars: Qui-Gon Appears As A Vision To Obi-Wan and Anakin On Mortis
A few years later in the middle of The Clone Wars, Obi-Wan, Anakin, and Anakin's new padawan, Ahsoka Tano, would find themselves drawn to the Star Wars' oherworldly and supernatural planet of Mortis, a world separate from the rest of the galaxy possessing a massive connection to the Force itself. Its three inhabitants were the immensely powerful Son, Daughter, and Father, serving as representations of the dark and light sides of the Force and the balance between the two.
During the three-episode arc featured in Clone Wars' third season, Qui-Gon appeared before Obi-Wan (voiced by Liam Neeson). After asking Obi-Wan if he had trained Anakin, Qui-Gon explains Mortis' existence as "a conduit through which the entire Force of the universe flows." He also warned Obi-Wan of the danger Anakin is in should he fail to achieve balance within himself, seeing as how the three Force beings all believe Anakin to be the Chosen One (just as Qui-Gon does).
Clone Wars: Yoda Learns About The Living and Cosmic Force From Qui-Gon
Near the end of The Clone Wars, Qui-Gon began speaking to Jedi Master Yoda, summoning him to the world of Dagobah so that he could help the Grand Master begin the next phase of his training. While Qui-Gon didn't appear in person as a Force ghost in Star Wars due to his own training in the Cosmic Force being incomplete (the Mortis version of Qui-Gon being a vision), Jinn leads Yoda to the Force Priestesses who begin to show him the secrets of the Cosmic Force in this sixth season arc featured in Clone Wars.
Through Qui-Gon, Yoda was likewise able to learn how to retain his consciousness after death, explaining how he was able to return as a Force ghost in Return of the Jedi. Likewise, Yoda helps Obi-Wan learn the same knowledge for himself as revealed at the end of Revenge of the Sith, teaching him how to commune with Qui-Gon and learn the secrets of the Cosmic Force so he might begin his training while in exile on Tatooine.
Star Wars: Rebels: Qui-Gon's Voice In The World Between Worlds
A few years prior to A New Hope, the young Jedi/Rebel Ezra Bridger finds himself in the World between Worlds in the final season of Star Wars Rebels. Having access to certain points in time and space thanks to the Cosmic Force, Ezra was able to reach into the past to save Ahsoka from her duel with Darth Vader. However, the two Jedi are forced to escape the interdimensional realm before Emperor Palpatine could use them to enter the World between Worlds which he would have no doubt used to gain even greater power.
During his time in the supernatural realm, Ezra hears a cacophony of voices: lines of dialogue from all over the Star Wars timeline. Not only were these lines from the past and present, but some were even from the future such as the voices of Rey and Kylo Ren in the sequel trilogy. However, Qui-Gon's line from The Clone Wars is heard about Mortis being a conduit of the Force. This makes sense seeing as how the entrance to this realm was a mural of the Son, Daughter, and Father, as well as the fact that the World between Worlds is clearly another powerful conduit in the Force as well.
Rise Of Skywalker: Rey Hears Qui-Gon Jinn's Voice
Last but not least, Qui-Gon's voice was among the multitude of Jedi voices who reached out to Rey in The Rise of Skywalker during the final confrontation with the Emperor on Exegol. Receiving their guidance and encouragement as she faced Palpatine, Qui-Gon confirmed that Rey had never been alone: "Every Jedi who ever lived lives in you." This gave Rey the strength she needed to defeat Palpatine once and for all in the final episode of the Skywalker saga.
While this is every appearance where Qui-Gon is either seen or heard on screen so far, it's possible that he could have a new appearance in the upcoming Obi-Wan Kenobi series coming soon to Disney+. Novels have already confirmed that Obi-Wan did succeed in communing with his master while in exile on Tatooine, and the two Jedi even spoke face to face with Qui-Gon as a Force ghost, having eventually completed his own training. In any case, after all of these appearances, it's pretty clear that Qui-Gon Jinn is one of Star Wars' most influential Jedi ever especially after his death.